1. The Field of the Invention
The field of the invention relates to an improved fastener assembly useful in securing insulation materials to a deck in which the deck is made of a porous or fibrous material such as gypsum or wood. More particularly the invention relates to a combination of a stress plate with a buttress thread type fastener.
2. Description of the Prior Art
Backout by uplift or rotation of a fastener installed in a stress plate to hold down insulation on a roof is an ongoing problem in the roof installation trade. Many attempts in the prior art have been made to solve the problem without successor only partial success.
The prior art is best demonstrated by U.S. Pat. No. 4,892,429 (Jan. 9, 1990 to Giannuzzi) which discloses but does not claim a buttress thread-type fastener on the underside of whose head is formed a pawl which mates with a ratchet arrangement formed on the perimeter of the annulus of a stress plate. During installation the pawl does not resist rotation and seats itself locked in the ratchet at maximum torque. Anti-backout is provided to some extent thereby. In service, it is possible for the ratchet tooth which is essentially coplanar to the stress plate to cut into and through the pawl since the plate is generally of metal and the fastener of 30% glass reinforced nylon. It is presumed that the disclosed subject matter is still part of a continuing patent application.
NTB Fastening Systems, Inc., Mosinee, Wis., provides its "Magnum (.TM.)" system utilizing a plastic washer insert having fingers disposed radially inward about its annulus. These hold a buttress thread fastener in assembly relationship with a stress plate to facilitate installation. During installation the fingers, made of materials as soft or softer than the fastener are meant to deform and are not capable of providing anti-backout, or anti-rotational forces.